Method of manufacturing continuous sucker rod

ABSTRACT

A method for manufacturing a continuous sucker rod coil, wherein the method includes the step of selecting a plurality of input coils, each input coil having the same uniform hardness, and each input coil having two free ends. The method further includes the step of fusing adjacent free ends of adjacent input coils together to form one continuous length of rod, the fusing creating fused areas and a heat-affected zone at each fused area. The method also includes the step of treating each of the heat-affected zones to alleviate irregularities induced during fusing. Additionally, the method includes the step of winding the continuous length of rod into a finished coil.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 13/648,141, filed Oct. 9, 2012, which is a continuation of U.S.patent application Ser. No. 10/518,620, filed Jan. 20, 2006, now U.S.Pat. No. 8,281,472, which is a 371 of PCT/CA2003/000981, filed Jun. 27,2003. The aforementioned applications are herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a simplified method and apparatus formanufacturing continuous sucker rods.

2. Description of the Related Art

In oil and gas wells, a “drive string” connects the pump, located downhole, to the drive system, located at the surface. Conventional suckerrods are elongated steel rods, 20 feet to 30 feet in length. Traditionaldrive string typically consisted of a sequence of conventional suckerrods with connecting mechanisms at each end of each conventional suckerrod which permit end-to-end interconnection of adjacent rods. Incontrast, continuous sucker rod is a unitary rod, consisting of oneelongated continuous piece of steel. Thus, continuous sucker rod doesnot have the numerous interconnection points found in the interconnectedconventional sucker rods. Each interconnection point between twosuccessive conventional sucker rods is a source of potential weaknessand excess wear on the adjacent tubing and casing. However, increasedcosts can be associated with continuous sucker rod.

The length of a drive string can vary from anywhere from as little as500 feet to as much as 10,000 feet or more, depending on the depth ofthe well and desired location of the pump down hole. Continuous suckerrod is typically produced and stored for sale on large transport reels.These transport reels have a maximum diameter of about 19 to 20 feet andthe diameter may be as small as 9-10 feet. (The desired maximum diameteris limited by transport issues). A full reel can carry continuous suckerrod with lengths of over 6,000 feet depending on the diameter of therod.

The properties of the steel used for any drive string sucker rod,whether continuous or conventional sucker rod depend upon the conditionsof the well and the drive system and pumping system used to produce thewell. Sucker rod is generally classified into grades which are suitableover a range of load conditions and/or environmental conditions, such asH.sub.2S content of the well. The design of continuous sucker rod mustbe such that the continuous sucker rod can be wound tightly enough tofit snugly on the transport reel and then be able to be straightenedinto a drive string at the well, without sacrificing the desiredproperties for the load and environmental conditions of the intendeduse. Winding the continuous sucker rod onto transport reels sometimescauses permanent deformation as the rod is wrapped onto the transportreel and then straightened in the field for use.

Palynchuk, Canadian Patent No. 942,585 discloses one of the originalmethods of manufacturing continuous sucker rod. In Palynchuk, continuoussucker rod was made by taking a series of input coils, joining the endsof the coils together, and subjecting the joined coils to a series oftreatment steps. The coils were also hot worked from a roundcross-section to oval cross-section along the entire length of thecontinuous sucker rod. The oval cross-section permitted the continuoussucker rod to be wrapped on the transport reel in the direction of itsminor diameter which reduced the extent of permanent plastic deformationin the continuous sucker rod. Oval cross-sectional continuous sucker rodis generally used with reciprocating pump applications.

Heavy oil wells are most often produced with progressive cavity pumps(“PC Pumps”). PC Pumps are driven by a rotary drive and consequently,the drive string used in these applications also rotates. Ovalcross-section sucker-rod is not suitable for rotating drive stringapplications due to the eccentric loads encountered during rotation andgreater wear caused along the tubing. Also, the effects of plasticdeformation on sucker rod performance are less of a concern withrotating drive strings because the loads are torsional and the rotatingdrive strings are not subjected to the cyclical high compression/tensionloads experienced in the reciprocating pump applications. Therefore,expensive oval cross-section continuous sucker rod, such as thatdisclosed by Palynchuk, is not generally used for rotary driveapplications. Round cross-sectional sucker rod and continuous suckerrod, is more suitable.

Steel used to make continuous sucker rod is received from the steel millin raw coils. The steel is manufactured by the steel mill to meetspecifications as directed by the sucker rod manufacturer. Steelmanufactured to ASTM standard A576 and supplementary requirements S7,S8, S11, S12 and S18 is known to produce suitable sucker rod for mostoil and gas applications. To meet these requirements, the input coilsare specially alloyed using known techniques to produce a grade of steelwith suitable hardenability, strength, toughness, corrosion resistance,fatigue resistance, micro-cleanliness, and weldability.

However, the hardness and corresponding tensile strength of the steelcoils received from the mill in raw form is inconsistent, highlyvariable along individual coils and from coil to coil, and relativelylow. Since tensile strength is one of the most critical requirements forall sucker rod, it is necessary for the entire length of the steel coilsto be subject to treatment during the manufacture of the continuoussucker rod to ensure that the critical tensile strength requirements aremet and are uniform along the length of the continuous sucker rod. Inputcoils received from the steel mills in prior art practices are generallyof very low hardness due to the chemistry and manufacturing processesused in the steel mill.

Usually, a number of the raw coils must be fused together end-to-end toform one continuous sucker rod of the desired length. The ends areusually fused together by welding which creates heat-affected zonesadjacent to the welded area which must be treated to relieve stressesand yielding caused by the welding process. Without such treatment, theheat-affected zones would be a source of potential weakness which couldcause failure of the continuous sucker rod in use.

Prior art methods treat the entire length of the rod with a series ofaustenizing, quenching, and tempering treatment steps which produce afinal continuous rod which is of consistent hardness and strength andwhich also alleviate the problems induced by the welding in theheat-affected zone. The rod must be straightened and many of these stepsare to be applied along the entire length of the rod. Usually, two orthree successive production lines are required to subject the continuoussucker rod to all of the necessary steps, with the rod being uncoiled,straightened, treated as it passes through each line, coiled,transferred to the beginning of the next line, uncoiled and straightenedto pass through the next line, and so on.

These prior art methods of manufacturing continuous sucker rod thereforerequire extensive heavy, permanent equipment and a large fixed facilityto practice the method within. Steps such as ambient cooling necessitatea long open space within the manufacturing facility to permit the lengthof rod to be exposed for the requisite period of time and some presentfacilities in which the prior art methods are practiced can be as longas 300 feet or more. As a result, these prior art methods involvesignificant capital investment.

Recent methods have sought to reduce this capital investment by using 40foot rods transported directly to the well site and fusing them togetherwith a “portable” plant at the well site itself (see Widney et al, CA P2,317,291). Such methods are disadvantageous in that they are highlylabour intensive at remote locations.

What is needed then is a method of manufacturing continuous sucker rodwhich reduces the number of treatment steps required to be performedwithout sacrificing essential properties required to make the rodsuitable for load and environmental conditions as specified. It wouldalso be preferable to have a method which permits reduced capitalinvestment into equipment and facilities, thereby reducing costs.

SUMMARY OF THE INVENTION

The present invention satisfies the aforementioned needs of continuoussucker rod manufacturers as well as other needs.

A method of manufacturing a continuous sucker rod coil is provided whichcomprises the steps of: (a) selecting a plurality of input coils, eachinput coil having the same uniform hardness, and each input coil havingtwo free ends; (b) fusing adjacent free ends of adjacent input coilstogether to form one continuous length of rod, said fusing creatingfused areas and a heat-affected zone at each fused area; (c) treatingeach of said heat-affected zones to alleviate irregularities inducedduring fusing; (d) winding said output coils into a finished coil.

The method can alternatively be comprised of the steps of: (a) selectingone or more input coils each with the same consistent hardness, eachinput coil having two free ends; (b) inspecting said input coil forflaws; (c) marking said flaws; (d) removing said flaws creating furtherfree ends in said input coil; (e) fusing adjacent free ends together toform one continuous length of rod, each of said fusing creating a fusedarea and a heat-affected zone at each fused area; (f) treating each ofsaid heat-affected zones to alleviate irregularities induced duringfusing; (g) winding said output coils into a finished coil.

This method eliminates heavy equipment and reduces space and timerequirements thereby reducing capital costs and providing a transferablefacility.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a method for manufacturing continuous suckerrod known in the prior art;

FIG. 2 is a schematic of the method of manufacturing in accordancewithin the present invention; and,

FIG. 3 is a schematic of an alternative embodiment of method ofmanufacturing in accordance with the present invention.

DETAILED DESCRIPTION

The prior art method shown in FIG. 1 is an illustration of the stepsinvolved in a prior art method where the steel from the steel mill isselected without specifying a requirement of a uniform tensile strengthalong and among the input coils to be used to produce the continuoussucker rod. Referring now to FIG. 1, there are three lines in thismethod—Line 1 (50), Line 2 (60) and Line 3 (90).

On Line 1, the steel coil from the steel mill (not shown) is uncoiled byan uncoiler (52), then straightened by a straightener (54) and thenpassed through a first flash-butt welding section (56). Welding in thefirst flash-butt welding section (56) is applied only to the ends of thesteel mill coils to fuse one end of one coil to the end of the next coilto form one continuous elongated piece of steel. After passing throughthe flash-butt section, the steel is transferred to a large working reel(58) to be held until production on Line 2 is initiated.

On Line 2 (60), the steel is rolled off of the working reel (58), andfirst passes through a water descaling section (62), then through a heattreatment section (64). The heat treatment section (64) includes aninductor (66) for austenizing the rod, rolling mills (68) for rolling toreduce the cross-section of the rod if necessary, a quenching section(70), a second inductor (72) for heating, and an ambient cooling section(73) and cooling tank (74) for cooling. The purpose of the steps in theheat treatment section (64), apart from the rolling mills (68), is tocause the steel to undergo the structural transformations at the atomiclevel that create the critical uniform hardness and resulting tensilestrength required for the specified load and environmental conditions inthe field. As can be seen in the FIG. 1, the heat treatment section (64)itself includes a number of pieces of heavy equipment and requires asignificant amount of space. After passing through the heat treatmentsection (64), the steel continues on Line 2 through a shot-peeningsection (76) and an eddy current section (78) for flaw detection andthen is transferred to a finished goods reel (80).

On Line 3 (90), a number of finishing steps are performed, includingremoval of flaws that have been identified on Line 2. Line 3 (90)includes a flash-butt welder (92), mini-heat treating station (94) and acorrosion coating section (96). After completion in Line 3, thecontinuous sucker rod is transferred to a transport reel (98) fortransport as directed by the customer.

Referring now to FIG. 2, the preferred embodiment of the manufacturingmethod in this invention is described below.

The method begins with the selection of the material for the input coils(10) which is a critical step. The input coils (10) are received fromthe steel mill in hot rolled condition of desired diameter and specifiedcross-section, such as round cross-section. The input coil (10) is of acomposition known to be suitable for sucker rod. Preferably, the inputcoils (10) are hot rolled steel manufactured as Special Bar Quality asspecified in ASTM A576 and supplementary requirements within ASTMA576—S57, S8, S11, S12 and S18 to meet known requirements for steel thatwill perform well as sucker rod, but other standards and specificationsknown to produce suitable sucker rod could also be used. However, inthis invention the selection of the raw material for the input coils(10) includes an additional requirement—the as-rolled hardenabilitycharacteristic of the input coils (10) must be uniform longitudinallyand cross-sectionally along and among the input coils to be joinedtogether and be at a specified limit within a specified range to ensureuniform minimum tensile strength. This differs from the prior art whereuniform hardness and corresponding tensile strength within a specifiedrange or limits for the input coils (10) are not specified.

Conveniently, the input coils (10) can be selected to correspond to anumber of grades as per current industry practice to provide reasonableproduct variation. The number of grades and corresponding ranges arematters of choice depending on convenience of providing multiple grades(a production and inventory issue). The choice of grade will depend onthe particular application the drive string is to be used for.

The minimum tensile strength required for any given applications will begoverned by the maximum load conditions expected to be encountered inuse. Since it is well-known that exposure to H.sub.2S causes failure ofsteel sucker rod when hardness exceeds a certain limit, potentialexposure to H.sub.2S provides a maximum upper limit on the permittedhardness, and therefore the maximum tensile strength of the sucker rod,if the sucker rod is to be used in H.sub.2S service. Costs, whichtypically increase with higher strength rod, are also a consideration.

The hardness and tensile strength specified for the input coils can beachieved by the addition of known alloying elements, such as Boron,Chromium, and the like, in accordance with known techniques. The choiceof the alloying elements and the methods to be used will be dictated bythe individual steel mill facility and its process which are the sourceof the input coils. Previously, the steel mills producing input coilsfor prior art methods did not need to include these considerations inthe production of the input coils because consistent hardness andcorresponding tensile strength of the input coils were not specified asrequirements. Of course, the alloys chosen and techniques used must notunduly affect other desired properties for suitable sucker rod asspecified.

Hardenability gauges the propensity of a steel to harden in depth andbreadth. Hardening of steel is facilitated by cooling steel rapidly froma critical temperature. Hardening is achieved by the addition ofelements which promote hardening, such as Carbon, Manganese, Chromium,Nickel and-Boron. Carbon and Manganese-are-common due to costeffectiveness. Recently developed “micro-alloyed” steels use Titanium,Vanadium and Columbian in very small quantities. Hardness ensuresstrength which is a key design parameter in the design of a rod string.The material hardness (strength) of continuous sucker rod needs toprovide adequate resistance to imposed stresses.

Ultimate Tensile Strength (UTS) is the highest load the material willbear. UTS is proportional to hardness and is achieved in the same way ashardenability. Yield strength is the elastic limit of the material.Yield strength is a characteristic of the micro-structure of the rod andtwo materials with the same UTS but different micro-structure mayexhibit different yield strength. Alloying the material will enhance theformation of a micro-structure which will exhibit a higher UTS/yieldstrength ratio. Micro-alloying elements may be used to gain both typesof strength and the ratio between them. Continuous sucker rods aresubjected to relatively high loads and therefore a suitably high UTSmaterial should be used. A material with a higher UTS/yield strengthratio will result in a tougher rod (in the sense of requiring moreenergy to fail) and may exhibit better fatigue properties.

Steel is made up of grains on a microscopic level. Finer grained steelsare tougher and stronger than coarse grained steels. There are a widevariety of methods to achieve fine grained steels. Alloying has beenused in this invention to inhibit grain growth, although there is nodata to indicate that such method is preferred. Hot rollingCarbon-Manganese steels micro-alloyed with Vanadium at lower rollingtemperatures will enhance grain size. Finer grains will provide enhancedtoughness and fatigue resistance and will exhibit less tendency to failalong grain boundaries.

Where flash-butt welding is anticipated as part of the overall method ofmanufacturing, Carbon is an unfavourable choice of hardening element dueto the possibility of embrittlement or decarburization during theflash-butt welding process which could lead to an undesirable weak orbrittle weld joint. A Vanadium enhanced Carbon-Manganese steel hastherefore been tested in accordance with this invention. Such a steelprovides strong welds with properties more uniform to the parent rod.

Fatigue loading is the application of repeated load over an extendedperiod of time where the load is well under the tensile strength of thematerial. Fatigue failures are progressive and often start from asurface flaw. After a number of load reversals, a crack may initiate andpropagate through the cross-section. Micro-alloying, rolling practicesand heat treatment may enhance fatigue properties. Vanadium additionsmay lead to a fine grained steel with enhanced fatigue properties.Continuous sucker rod often-fails in fatigue mode. Enhanced fatigueresistance will therefore tend to increase the service life of the rod.

Different steels will corrode at different rates when subjected tocorrosive environments. Typical oil well corrosion is via electro orchemical mechanisms. Alloying is also frequently used to creatematerials with enhanced corrosion resistance in the oilfieldenvironment. Carbon-Manganese based steel is one material generallyaccepted in the industry as being suitable for the oilfield environment.Reasonable corrosion resistance will enhance the service life of thecontinuous sucker rod.

Testing and field trials have been conducted using a Carbon-ManganeseSteel micro-alloyed with Vanadium and Niobium obtained from Stelco Inc.of Hamilton, Ontario, Canada identified as 1.031 Grade X.

Once input coils are selected in accordance with the requirements, theremainder of the method of the preferred invention is enabled.

Referring again to FIG. 2, an input coil (10), selected and receivedfrom the steel mill in accordance with the above requirements, is setinto the staging area of the processing facility for a pre-processinginspection. The input coil (10) is visually inspected for surface flawsand bends. If these flaws are found to be outside of specifications,they are to be marked for subsequent cut-out or re-work. If the densityof the flaws is severe, the input coil (10) may be scrapped prior toprocessing.

The input coil (10) is placed on the mandrel of an uncoiler (12) and thesteel shipping bands (not shown) are removed. The uncoiler (12) supportsthe input coil (10) during the uncoiling operation and facilitates theorderly uncoiling of the raw material without tangling and kinking. Theuncoiler (12) is used to uncoil the input coil (10) in a known manner.

After uncoiling, the rod passes through a two axis, multi-roll rodstraightener (16) which performs a cold straightening operation.Preferably, the coiled steel material is straightened dynamically in thevertical and horizontal axis such that even relatively high yieldstrength material is successfully straightened to an industry standard,such as API 11B for example, (which is, for a gauge length of 12 inches,the maximum allowable bend is 0.065″ or 0.130″ total indicated runout(TIR)). The straightener (16) acts to straighten and propel the rodforward in a known manner, yielding the rod in the opposite direction tothe bend of the steel in it's coiled as received form in the input coil(10). Proper straightening of the rod during manufacture prevents therod assuming a “wavy” form after being wound onto the transport reel andthen off the transport reels to form a drive string in the field.Although wavy rod will perform under some conditions, straight rod isgenerally required by customers and is a more desirable and marketableproduct.

Upon leaving the straightener (16), the rod is passed through aflash-butt welding section (20). The flash-butt welding section (20)includes an automatic flash-butt welding machine (21). Each input coil(10) will have a free end at the beginning and at the end of the coil.Additional free ends within the input coil (10) will be created when aflaw marked for cut-out is cut out (discussed below). The cut-out isperformed using a shear or cutting torch (not shown). The flash-buttwelding machine (21) is used to fuse adjacent free ends of the inputcoil ends (14) together to form one continuous rod, whether those freeends are adjacent ends from either side of a flaw cut-out or fromadjacent free ends of one input coil to the next input coil in theseries.

Flash-butt welding fuses the free ends together in the following manner.Adjacent free ends are clamped in an axially opposing manner by twoelectrodes of opposite electrical polarity. One electrode is fixed whilethe other moves in the axial direction. When the electrodes areenergized, the rod becomes the electrical conductor of a high current.The electrical current flowing through the rod is converted to heat dueto the electrical resistance of the rod. The rod ends heat to themelting temperature of steel for a brief period before they are rapidlyforced together under the action of the moveable electrode. The fusingprocess of the welding creates a fused area and a heat-affected zone.The heat-affected zone typically extends throughout the fused area and 1to 2 inches on either side of the fused (welded) area. The welded rod isheld in the upset position briefly while the heat-affected zone of thefused area cools. Upon cooling, the electrodes are unclamped and theheat-affected zone is ground and polished to meet rod body dimensionalspecifications.

After cooling, the heat-affected zone adjacent each weld must be treatedto alleviate imperfections induced by the flash-butt welding. Thistreatment occurs in the flash-butt welding section (20). Theheat-affected zone is reclamped in the electrodes of the flash-buttwelding machine (21) and tempered for stress relieving in a knownmanner. As an example, the heat-affected zone may be heated to560.degree. C., a temperature well below Acl (the temperature at whichaustenite begins to form during heating) held for a stress relievingtime of approximately 30 seconds, after which the heat-affected area isair-cooled in ambient conditions. Stress relieving ensures the weld areais made free of residual stresses induced during the weld process. Afterthe stress relieving process is complete, all welds are inspected forcracking and incomplete fusion using a standard magnetic particleexamination procedure.

After the flash-butt welding of the free ends is complete, the fused rodis transferred out of the flash-butt welding section (20).

Though not necessary in all applications, the rod exiting the flash-buttwelding section (20) is preferably immediately fed through a multi-wheelshot-peening apparatus (22). The shot-peening apparatus (22) removes theiron oxide covering the steel and mechanically peens the outside surfaceof the rod. Sucker rods commonly fail under a fatigue mode of failuredue to the propagation of tiny surface defects, notably cracks. Sincecracks will only propagate under tensile stress, the crack tips will notopen further if a net compressive stress remains on the crack tip asinduced by shot-peening and therefore the continuous sucker rod life isextended and improved fatigue resistance due to the induced compressivestress on the rod surface is achieved. As well, mill scale covering onthe raw steel may offer a preferential site for the start of crevicecorrosion if not removed. Crevice corrosion is a localized form ofcorrosion associated with small volumes of stagnant solution, in thiscase, pockets created by the loosely attached mill scale. Shot-peeningalso effectively removes the mill scale and ensures a clean surface,free of areas susceptible to preferential corrosion. However, it is tobe understood that other methods of cleaning the mill scale and/orplacing the surface of the rod into compression may be used and that theenhanced crack resistant product resulting from shot-peening, althoughis an improved product, is optional.

After exiting the shot-peening operation, the rod is then, optionally,surface inspected using an on-line eddy current flaw detector (23). Ifsufficiently significant, the flaws are marked with flaw markingequipment (24) for cut-out. Alternative known means of flaw detectionare also available. However, eddy current inspection is preferred due toits repeatable results and relative ease of application to continuousinspection.

As each flaw is marked and identified, the rod is stopped and backed upto the flash-butt welding section (20). A shearing or cutting torchlocated in the flash-butt welding section (20) is used to cut out theflaws, creating two new free ends which must be fused together using theflash-butt welding machine (22) in the same manner that the free ends ofthe coils were fused. The new weld will then pass through theshot-peening apparatus (22) and the eddy-current flaw detector (23) tobe re-inspected.

It will be apparent that the rod will run continuously through theuncoiler (12) and the straightener (16) and will not be stopped as itpasses through the flash-butt welding section (20) the first time unlessa free end of the input coil (10) is encountered. The free end of oneinput coil (10) will be fused to the adjacent free end of the next inputcoil (10) in series which will have passed through the uncoiler (12) andthe straightener (16) in the same manner as the input coil before it.Rod passing freely through the flash-butt welding section (20) willcontinue to pass continuously through the shot-peening apparatus (22)and the eddy current flaw detector (23). If, however, a flaw is markedfor cut-out during the flaw detection by the eddy current flaw detectorthen, the process must be stopped, and the rod backed up to place theflaw at the beginning of the flash-butt welding section (20) where theflaw is removed as described above, creating two further adjacent freeends which must then be welded by the flash-butt welding machine (20)creating heat-affected zones which are treated as described above. Afterthat, the rod begins to run continuously again so that the fused areaand heat-affected zone (where the weld was) pass through theshot-peening apparatus (22) and are themselves inspected for flaws withthe eddy current flaw detector (23). Backup to the flash-butt weldingsection (20) can be repeated if further flaws, in the fused area andheat-affected zone or elsewhere along the rod, are detected. Otherwise,the rod will pass to the next section.

The steps of inspecting and marking for flaws and then backing up therod for removal of those flaws, although preferable, are optional.

The rod is accurately measured linearly upon exit of the process bymeans of wheel mounted digital encoder (25) running on the moving rod,or other suitable device. Accurate length measurements ensure individualrod strings are to customer's requirements and bulk reels of rod complywith road transportation weight limits.

After measurement, the rod is driven through a bath of atmosphericcorrosion inhibitor (26), which prevents the rusting of the continuoussucker rod while stored in inventory. The inhibitor is pumped over themoving rod and the excess coating is wiped away prior to exiting thecoating enclosure. The coated rod is then guided through a series ofrollers which wind the rod onto transport reel (28) into a finished coil(30) for storage in inventory and safe shipment to the field well site.

The finished coil (30) has a specified limit or range of yield strength.The finished coil (30) is suitable for use as drive string for rotarypump applications where the specified yield strength is sufficient tomeet the maximum load conditions expected to be experienced in use. Thefinished coil (30) may also be suitable for use in reciprocating pumpapplications where fatigue resistance is of minimal concern.

In an alternative embodiment, it may be possible to avoid backing up therod to before the flash-butt welding section (20) after flawidentification at the eddy current flaw detector (23) occurs by placingan additional flash-butt welding section immediately after the eddycurrent flaw detector (23). In this case, free ends of adjacent inputcoils would be joined at the flash-butt welding section (20) whilecutting out the flaws and fusing the further free ends that are formedby the cutting out process would occur in the second flash-butt weldingsection. In this embodiment, the fused areas formed in the secondflash-butt welding section would not be shot-peened or themselvesinspected for flaws.

In another alternative embodiment, it may be possible to place theshot-peening apparatus (22) and the eddy-current flaw detector (23)before the flash-butt welding section (20). This is illustrated in FIG.3. However, if the welds are also to be shot-peened and inspected(preferable), the rod would have to be backed up prior to bothoperations in order for the heat-affected zone of the weld to besubjected to these treatment steps.

It will be apparent from the previous description that the currentinvention provides a number of distinct advantages over previous methodsof manufacturing continuous sucker rod. The method of the inventiondiffers from previous methods for manufacturing continuous sucker rodwhere the input coil is received in raw form with variable strength andhardness and where the desired consistency in strength and hardness isprovided by the series of austenizing, quenching, and tempering stepsapplied to the entire rod (as demonstrated from Line 2 in FIG. 1 of theprior art process). By selecting an input coil with the desired tensilestrength and uniform hardness characteristics, complicated, expensive,and time-consuming steps need not be applied to the length of the entirerod. Instead, a more limited tempering and cooling process is applied tothe heat-affected zone of the welds for more limited purposes. Since theheat-affected zone is limited to 1 to 2 inches on either side of eachweld, only a few feet in total must be treated, as opposed to the entirelength of the continuous rod and the treatment steps for theheat-affected zone are relatively simple and quick. As well, less labourper foot of rod manufactured is required.

Thus, the equipment required to practice this method is significantlyless cumbersome and fixed than that needed for previous methods. Onlyone production line is required. Only one flash-butt welding machine isrequired. Only one uncoiler and straightener is used. There is no needfor a long open air area for ambient cooling of significant lengths ofrod, thus required length of the facility is greatly reduced. There isno need for any of the heavy equipment used in the austenizing,quenching and tempering steps.

Consequently, the size and length of the facility can be significantlyreduced. Furthermore, all of the equipment required to practice themethod could be encompassed in a set of trailers, allowing for transferof the equipment to permit performance of the manufacturing method indifferent locations, including the field itself if desired. Thus, thesimplified facility could be transferable instead of fixed in apermanent structure. Even if practiced within a permanent structure, thelocation of the facility could be transferred with a relatively lowdegree of difficulty.

Thus, there is a significant reduction in the capital investmentrequired for the equipment and facilities used to perform thismanufacturing process. It is estimated that the capital costs could beas much as 90% lower than current costs.

Immaterial modifications may be made to the invention described herewithout departing from the essential characteristics of the invention.For example, it is not necessary to include ASTM standard A576 and anyor all of its supplementary requirements S7, S8, S11, S12 and S18,provided material suitable for use as sucker rod is chosen. As well,alternate methods of welding can be used. So too, alternate methods ofplacing the surface into compression and removing mill scale can be usedin place of shot-peening and alternate flaw detection methods can beused in place of eddy-current detection. As mentioned, it may not benecessary to straighten the rod during the process for some cases, butgenerally straightening results in a better performing, more marketableproduct. Similarly, it may not be necessary to include the shot-peeningand/or flaw detection and removal steps but both will enhance thequality of the final product. Although the rod contemplated in thepreferred embodiment is of round cross-section, it will be understoodthat other cross-section could be specified for the input coil and wouldbe received from the steel mill in the desired cross-section.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A system for manufacturing a continuous suckerrod coil, the system comprising: a single production line, comprising: acoil straightener configured to straighten input coils, each input coilhaving the same uniform hardness; a welding machine that is configuredto: fuse adjacent input coils together to form one continuous length offused input coils, wherein fusing creates a heat-affected zone at eachfused joint; and treat the heat-affected zones to alleviateirregularities induced during fusing, wherein the welding machineselectively treats sections of the fused input coils to form treatedsections and untreated sections; a flaw detection system for inspectinga surface of the straightened coils; a surface treating machineconfigured to clean a surface of the input coils and induce compressivestress in the surface; and a transport reel to receive the continuouslength of fused coils.
 2. The system of claim 1, wherein the singleproduction line consists of a single welding machine.
 3. The system ofclaim 1, wherein the welding machine receives the straightened inputcoils directly from the coil straightener.
 4. The system of claim 1,wherein the surface treating machine receives the input coils directlyfrom the welding machine.
 5. The system of claim 1, wherein the flawdetection system receives the straightened coils directly from thesurface treating machine.
 6. The system of claim 1, wherein the surfacetreating machine receives the input coils directly from the coilstraightener.
 7. The system of claim 1, wherein the flaw detectionsystem comprises an eddy current sensor.
 8. The system of claim 1,wherein welding machine receives the straightened coils directly fromthe flaw detection system.
 9. The system of claim 1, wherein the weldingmachine is a flash butt welder.
 10. The system of claim 1, wherein thestraightener is a cold straightener.
 11. The system of claim 1, furthercomprising flaw marking equipment and a digital encoder.
 12. The systemof claim 1, wherein the flaw marking equipment is positioned downstreamof the welding machine.
 13. The system of claim 1, wherein the flawmarking equipment is positioned upstream of the welding machine.